In this specification, the various terms in use for the film making techniques commonly referred to as “blue-screen”, “greenscreen”, “blue screen chroma-keying”, “greenscreen chroma-keying”, “traveling matte composite”, “keying”, and similar terms, will be referred to hereafter as “keying”.
Keying technology is well known in the prior art. It is a filmmaking technique whereby actors or other subjects are filmed acting a scene in front of an evenly lit, monochromatic background surface to produce an initial image. The background surface will be referred to as a “greenscreen”. The term “film” will be used to mean “film”, “videotape”, “digitally capture”, “record” and similar terms used to describe recording of audiovisual data onto media. The background surface is commonly blue or green, but may also be red, magenta, or another color.
In post-production processing, the monochromatic background in the intended image is replaced through keying, a process in which a single color or a narrow range of colors from one image, for example the background screen color, is removed to reveal another image behind. This allows other film footage or computer generated imagery (“CGI”) to form the final background imagery used in the finished product, namely, the final film as it is intended to be seen by the viewing audience. Note that the term “background” is used to mean the area of the original image which is to be replaced, regardless of whether such area forms the background in the final product. The imagery used to replace the monochromatic background may comprise a photograph, video, or other visual content.
This keying process is commonly used in the film industry to enable an actor to appear in scenes which would otherwise be impossible, extremely difficult or very costly to obtain. For a blue screen, whatever appears in a scene that is colored blue is replaced by an image from another camera, usually taken at a different time and location, to create a composite image. Examples of scenes in which keying might be used may include scenes of a climber on Mt. Everest, a superhero flying through the air carrying a full sized school bus full of children, an astronaut floating in space, or a long destroyed ancient Roman city seemingly rebuilt in Europe.
For a large budget motion picture, a production company may require a department made up of 200 to 500 people employed as CGI artists working in a facility known as a rendering farm to create the CGI background and CGI elements that most modern motion pictures and production companies rely on to create the amazing sequences that audiences now consider essential in modern films.
Commonly, the greenscreen used in the film industry is a fabric or other material of a solid color. The fabric or other material may be comprised of a natural fibre, a synthetic, or a combination. In order to facilitate the work of the CGI artists, reference markings are desirable on the greenscreen. In the past, such markings have been painted on, obtained with pieces of adhesive tape, or comprised small objects affixed to the greenscreen with pins or other fastening means. These methods of marking present several disadvantages.
These disadvantages include destruction of the greenscreen through puncture, tape residue or paint markings, rendering the greenscreen unfit for reuse. Also, these techniques provide markings with irregular borders, resulting in less than optimal keying in post production.